1. Field of the Invention
The present invention generally relates to a semiconductor device and a method for forming the same, and more particularly, the present invention relates to the semiconductor device and the method for forming the same, having a borophosphosilicate glass film as an interlayer insulator.
This application is a counterpart of Japanese application Ser. No. 155220/1998, filed May 20, 1998, the subject matter of which is incorporated herein by reference.
2. Description of the Related Art
In general, a multi-level interconnection is used effectively to provide the advantage of high integration. In the multi-level interconnection, an interlayer insulator is formed between interconnections. A borophosphosilicate glass film as the interlayer insulator is used for planarization in VLSI circuit.
The borophosphosilicate glass film covers an active region of a semiconductor device such as a MOS transistor. Then, the borophosphosilicate glass film is reflowed using thermal treatment. As a result, the interlayer insulator having a smooth surface is formed.
However, phosphorus in the borophosphosilicate glass film is diffused to the active region of the semiconductor device during reflow. It is desirable to avoid the outdiffusion of the phosphorus to the active region of the semiconductor device.
An object of the present invention is to provide a semiconductor device that can give an outdiffusion preventing function to an underlayer for phosphorus, of plural interlayer insulators including boron.
According to one aspect of the present invention, for achieving the above object, there is provided a semiconductor device comprising: a semiconductor substrate with an active region; an oxide film to cover the active region of the semiconductor substrate; a first borophosphosilicate glass film to cover the oxide film; and a second borophosphosilicate glass film to cover the first borophosphosilicate glass film; wherein the first borophosphosilicate glass film has a concentration of boron oxide which is lower than that of the second borophosphosilicate glass film.
An object of the present invention is to provide a method for forming a semiconductor device that can avoid the outdiffusion of the phosphorus to the active region of the semiconductor device.
According to another aspect of the present invention, for achieving the above object, there is provided a method for forming a semiconductor device comprising:
providing a semiconductor substrate with an active region; covering the active region of the semiconductor substrate with an oxide film; covering the oxide film with a first borophosphosilicate glass film having an inhibitory of an outdiffusion of the phosphorus; covering the first borophosphosilicate glass film with a second borophosphosilicate glass film including phosphorus and boron; and reflowing the second borophosphosilicate glass film so as to have a fluidity with thermal treatment.